Loss of gut barrier integrity triggers activation of islet-reactive T cells and autoimmune diabetes.

Low-grade intestinal inflammation and alterations of gut barrier integrity are found in patients affected by extraintestinal autoimmune diseases such as type 1 diabetes (T1D), but a direct causal link between enteropathy and triggering of autoimmunity is yet to be established. Here, we found that onset of autoimmunity in preclinical models of T1D is associated with alterations of the mucus layer structure and loss of gut barrier integrity. Importantly, we showed that breakage of the gut barrier integrity in BDC2.5XNOD mice carrying a transgenic T cell receptor (TCR) specific for a beta cell autoantigen leads to activation of islet-reactive T cells within the gut mucosa and onset of T1D. The intestinal activation of islet-reactive T cells requires the presence of gut microbiota and is abolished when mice are depleted of endogenous commensal microbiota by antibiotic treatment. Our results indicate that loss of gut barrier continuity can lead to activation of islet-specific T cells within the intestinal mucosa and to autoimmune diabetes and provide a strong rationale to design innovative therapeutic interventions in "at-risk" individuals aimed at restoring gut barrier integrity to prevent T1D occurrence.

MicroRNA-133b Regulation of Th-POK Expression and Dendritic Cell Signals Affect NKT17 Cell Differentiation in the Thymus.

NKT17 cells represent a functional subset of Vα14 invariant NKT (iNKT) cells with important effector functions in infections and autoimmune diseases. The mechanisms that drive NKT17 cell differentiation in the thymus are still largely unknown. The percentage of NKT17 cells has a high variability between murine strains due to differential thymic differentiation. For example, the NOD strain carries a high percentage and absolute numbers of NKT17 cells compared with other strains. In this study, we used the NOD mouse model to analyze what regulates NKT17 cell frequency in the thymus and peripheral lymphoid organs. In accordance with previous studies showing that the zinc finger transcription factor Th-POK is a key negative regulator of thymic NKT17 cell differentiation in the thymus, our data indicate that excessive NKT17 cell frequency in NOD mice correlates with defective Th-POK expression by thymic Vα14iNKT cells. Moreover, we found that Th-POK expression is under epigenetic regulation mediated by microRNA-133b whose expression is reduced in Vα14iNKT cells of NOD mice. We also demonstrated in a conditional knockout model of dendritic cell (DC) depletion (CD11cCreXDTA.B6 and CD11cCreRosa26DTA.NOD mice) that DCs play a crucial role in regulating Vα14iNKT cell maturation and their acquisition of an NKT17 cytokine secretion phenotype in the thymus. Overall, our data show that mechanisms regulating NKT17 cell differentiation are unique and completely different from those of Vα14iNKT cells. Specifically, we found that epigenetic regulation through microRNA-133b-regulated Th-POK expression and signals provided by DCs are fundamental for thymic NKT17 cell differentiation.

Increased iNKT17 Cell Frequency in the Intestine of Non-Obese Diabetic Mice Correlates With High Bacterioidales and Low Clostridiales Abundance.

iNKT cells play different immune function depending on their cytokine-secretion phenotype. iNKT17 cells predominantly secrete IL-17 and have an effector and pathogenic role in the pathogenesis of autoimmune diseases such as type 1 diabetes (T1D). In line with this notion, non-obese diabetic (NOD) mice that spontaneously develop T1D have an increased percentage of iNKT17 cells compared to non-autoimmune strains of mice. The factors that regulate iNKT cell expansion and acquisition of a specific iNKT17 cell phenotype are unclear. Here, we demonstrate that the percentage of iNKT17 cells is increased in the gut more than peripheral lymphoid organs of NOD mice, thus suggesting that the intestinal environment promotes iNKT17 cell differentiation in these mice. Increased intestinal iNKT17 cell differentiation in NOD mice is associated with the presence of pro-inflammatory IL-6-secreting dendritic cells that could contribute to iNKT cell expansion and iNKT17 cell differentiation. In addition, we found that increased iNKT17 cell differentiation in the large intestine of NOD mice is associated with a specific gut microbiota profile. We demonstrated a positive correlation between percentage of intestinal iNKT17 cells and bacterial strain richness (α-diversity) and relative abundance of Bacterioidales strains. On the contrary, the relative abundance of the anti-inflammatory Clostridiales strains negatively correlates with the intestinal iNKT17 cell frequency. Considering that iNKT17 cells play a key pathogenic role in T1D, our data support the notion that modulation of iNKT17 cell differentiation through gut microbiota changes could have a beneficial effect in T1D.